Since the introduction of communication systems such as mobile communication systems and mobile telephony networks, and the communication devices designed to work on such systems, including mobile stations such as mobile telephones, criminals and fraudsters have sought to commit crime against both network operators and consumers.
The theft of mobile telephones, for instance, is relatively commonplace due at least partly to the fact that mobile telephones are generally relatively easy to steal since they are relatively hard to secure.
To aid in combating mobile telephone theft many mobile phone standards, such as the widely used GSM standard, require that each mobile station or mobile telephone incorporates a unique hardware identifier, referred to in GSM as the international mobile equipment identity or IMEI. Mobile telephone networks may implement an equipment identity register (EIR) which classifies IMEI numbers using a white list, for valid IMEIs, a black list, for barred IMEIs, and a grey list, for IMEIs to be tracked. The EIR is interrogated, for example when a mobile telephone attempts to connect to a mobile telephone network, and access to the network may be prevented if the IMEI is found in a black list in the EIR.
The rationale of using an EIR was that mobile telephone theft could be significantly reduced by rendering stolen mobile telephones effectively useless. However, use of the EIR has been less effective at reducing mobile telephone theft than initially hoped due to increased criminal cloning of IMEI numbers. By cloning is meant the modification of the IMEI of one mobile communication device with the IMEI of another mobile communication device. Typically, cloning is performed to enable a stolen communication device, whose IMEI is blacked listed by an EIR, to assume the identity of a non-blacklisted communication device. Cloning in this manner is generally illegal in many countries.
Another common crime is the cloning of subscriber identifiers, known in GSM as international mobile subscriber identity (IMSI). In GSM systems the IMSI is stored on a subscriber identity module (SIM) smart card and uniquely identifies a subscriber or subscription in a GSM network. By cloning an IMSI a criminal can make calls which are charged to the subscriber whose IMSI has been cloned. IMSI cloning is problematic for both the owner of the genuine IMSI, who has to convince the network operator which charges were made fraudulently, and to the network operator who will ultimately foot the bill for any fraudulent use made.
Typically, use of a cloned IMSI is only detectable when the owner of the genuine IMSI notices that he has been charged for calls not made by him, by which time the fraud will have generally already been committed. The network operator is generally obliged to provide the genuine subscriber with a new SIM card containing a new IMSI, however this inflicts further inconvenience on the genuine subscriber.
Accordingly, one aim of the present invention is to overcome, or at least alleviate, at least some of the above-mentioned problems.